Backlight unit, down-conversion medium comprising the same and display device

ABSTRACT

Provided are a backlight unit, a down-conversion medium including the same, and a display device including the down-conversion medium. The backlight unit includes a light source configured to generate blue light; and an optical film configured to absorb a portion of the blue light generated from the light source to generate red light and green light, wherein the optical film includes a quantum dot matrix in which semi-metal element oxide is embedded.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2021-0133317 filed in the Korean IntellectualProperty Office on Oct. 7, 2021, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION (a) Field of the Invention

The present disclosure relates to a backlight unit including aerosolizedquantum dots, a down-conversion medium including the same, and a displaydevice including the down-conversion medium.

(b) Description of the Related Art

Recently, a material in which perovskite nanocrystals are encapsulatedwith various polymer materials such as polystyrene,polymethylmethacrylate, and the like has been proved to be applied as alight-emitting material in commercial LED devices, and currently,research on applying this material to a down-conversion medium (DCM) isbeing actively conducted. However, the down-conversion medium must use acolor filter in a prior art, but there is a problem of hardly improvingphoto efficiency due to the use of the color filter.

In addition, the light-emitting material uses an insulation polymer as amatrix, wherein the insulation polymer still has a problem of beinginherently vulnerable to thermal stress. In particular, long-termthermal stress may cause softening deformation or damage tothermoplastic polymers such as polystyrene, polymethylmethacrylate, acycloolefin copolymer, and the like.

SUMMARY OF THE INVENTION

An embodiment provides a backlight unit capable of improving patternprocessibility and photo efficiency.

Another embodiment provides a down-conversion medium including thebacklight unit.

Another embodiment provides a display device including thedown-conversion medium.

An embodiment of the present invention provides a backlight unitincluding a light source configured to generate blue light, and anoptical film configured to absorb a portion of the blue light generatedfrom the light source to generate red light and green light, wherein theoptical film includes a quantum dot matrix in which a semi-metal elementoxide is embedded.

The semi-metal element may include boron, silicon, germanium, arsenic,antimony, tellurium, fluorium, or a combination thereof.

The semi-metal element oxide may be silica.

The quantum dot may include Group 2-6 quantum dots, Group 3-5 quantumdots, Group 4-6 quantum dots, Group 4 quantum dots, Group 1-3-6 quantumdots, or a combination thereof.

The quantum dots may be Group 3-5 quantum dots.

The quantum dost may have a perovskite crystal structure.

The quantum dots may be metal halide-based quantum dots having aperovskite crystal structure.

The metal halide-based quantum dots having the perovskite crystalstructure may be represented by Chemical Formula 1.

ABX₃  [Chemical Formula 1]

In Chemical Formula 1,

A is an organic cation or inorganic cation,

B is a metal cation, and

X is a halide anion.

Chemical Formula 1 may be represented by CsPbX′₃, wherein X′ is Cl, Br,and/or I.

The metal halide-based quantum dost having the perovskite crystalstructure may be green quantum dots or red quantum dots.

The green quantum dots may be CsPbBr₃ and the red quantum dots may beCsPb(BrI)₃.

The quantum dot matrix in which the semi-metal element oxide is embeddedmay be aerosolized.

The aerosolization may be carried out under vacuum conditions.

An aerosol flow rate during the aerosolization may be about 0.1 L/min toabout 10 L/min.

The light source configured to generate blue light may be a blue OLED, ablue LED, or a blue EL device.

Another embodiment provides a down-conversion medium including thebacklight unit.

The down-conversion medium may be a color filter-free down-conversionmedium.

Another embodiment provides a display device including thedown-conversion medium.

Other embodiments of the present invention are included in the followingdetailed description.

The backlight unit according to one embodiment may greatly improvesphoto efficiency of the down-conversion medium without a color filterand thus ultimately improve photo efficiency of in a display deviceincluding the same by completely blocking a blue light leakagephenomenon, and furthermore, since a thin line width is realized, apattern process may be performed without a mask.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a process of manufacturing abacklight unit according to an embodiment.

FIG. 2 is a microscopic photograph of a backlight unit in whichsilica-embedded green quantum dots (CsPbBr₃) are aerosolized anddeposited on a blue OLED.

FIG. 3 is a photomicrograph of a backlight unit in which silica-embeddedred quantum dots (CsPb(BrI)₃) are aerosolized and deposited on a blueOLED.

FIG. 4 is a microscopic photograph of green quantum dots (CsPbBr₃)aerosolized and deposited on a blue OLED.

FIG. 5 is a microscopic photograph of alumina-embedded green quantumdots (CsPbBr₃) which are aerosolized and deposited on a blue OLED.

FIG. 6 is a microscopic photograph of silica-embedded green quantum dots(CsPbBr₃) which are aerosolized and deposited on a blue OLED.

FIG. 7 is a microscopic photograph of red quantum dots (CsPb(BrI)₃)which are aerosolized and deposited on a blue OLED.

FIG. 8 is a microscopic photograph of alumina-embedded red quantum dots(CsPb(BrI)₃) which are aerosolized and deposited on a blue OLED.

FIG. 9 is a microscopic photograph of silica-embedded red quantum dots(CsPb(BrI)₃) which are aerosolized and deposited on a blue OLED.

FIGS. 10 and 11 are graphs each independently showing the photoefficiency of the backlight unit according to Example 1, ComparativeExample 1, and Comparative Example 2.

FIGS. 12 and 13 are graphs each independently showing the luminance ofthe backlight units according to Example 1, Comparative Example 1, andComparative Example 2.

FIG. 14 is a graph showing the luminance (green) of the backlight unitaccording to Example 2.

FIG. 15 is a graph showing the luminance (green) of the backlight unitaccording to Example 1.

FIG. 16 is a graph showing the luminance (green) of the backlight unitaccording to Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention are described indetail. However, these embodiments are exemplary, the present inventionis not limited thereto, and the present invention is defined by thescope of claims.

As used herein, when specific definition is not otherwise provided,“substituted” refers to one substituted with a substituent selected froma halogen (F, Br, Cl, or I), a hydroxy group, a nitro group, a cyanogroup, an amino group (NH₂, NH(R²⁰⁰), or N(R²⁰¹)(R²⁰²), wherein R²⁰⁰,R²⁰¹, and R²⁰² are the same or different, and are each independently aC1 to C10 alkyl group), an amidino group, a hydrazine group, a hydrazonegroup, a carboxyl group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted alkynyl group, a substituted or unsubstituted alicyclicorganic group, a substituted or unsubstituted aryl group and asubstituted or unsubstituted heterocyclic group.

As used herein, when specific definition is not otherwise provided,“alkyl group” refers to a C1 to C20 alkyl group, and specifically a C1to C15 alkyl group, “cycloalkyl group” refers to a C3 to C20 cycloalkylgroup, and specifically a C3 to C18 cycloalkyl group, “alkoxy group”refers to a C1 to C20 alkoxy group, and specifically a C1 to C18 alkoxygroup, “aryl group” refers to a C6 to C20 aryl group, and specifically aC6 to C18 aryl group, “alkenyl group” refers to a C2 to C20 alkenylgroup, and specifically a C2 to C18 alkenyl group, “alkylene group”refers to a C1 to C20 alkylene group, and specifically 01 to C18alkylene group, and “arylene group” refers to a C6 to C20 arylene group,and specifically a C6 to C16 arylene group.

As used herein, when specific definition is not otherwise provided,“(meth)acrylate” refers to “acrylate” and “methacrylate,” and“(meth)acrylic acid” refers to “acrylic acid” and “methacrylic acid.”

As used herein, when specific definition is not otherwise provided,“combination” refers to mixing or copolymerization. In addition,“copolymerization” refers to block copolymerization or randomcopolymerization, and “copolymer” refers to a block copolymer or arandom copolymer.

In the chemical formula of the present specification, unless a specificdefinition is otherwise provided, hydrogen is boned at the position whena chemical bond is not drawn where supposed to be given.

In the present specification, when specific definition is not otherwiseprovided, “*” indicates a point where the same or a different atom orchemical formula is linked.

An embodiment provides a backlight unit including a light sourceconfigured to generate blue light; and an optical film configured toabsorb a portion of the blue light generated from the light source togenerate red light and green light, wherein the optical film includesquantum dots in which the semi-metal element oxide is embedded.

A conventional deposition method may be currently adopted to realize alarge area display but suffer from problems such as a process yield,mask warpage, and uniformity, and in order to solve the problems, aninkjet printing method is being discussed. Currently, the inkjetprinting method is adopted to coat quantum dots on a blue OLED substratebut suffers from problems such as nozzle clogging, non-uniform drying,difficulty in implementing a bank height, thickness increase of a colorconversion layer, a light leakage phenomenon, and the like.

Since these problems are caused by the color filter used in thedown-conversion medium (DCM), the inventors of the present inventionhave repeated numerous experiments and trial and error in order to makethe down-conversion medium usable without the color filter and solvedthe problems by coating nanocrystals in which the semi-metal elementoxide is embedded, for example, quantum dots on a light sourceconfigured to generate blue light, for example, a blue OLED substrate.

There have been prior attempts to use quantum dots in which an oxide isembedded, but no attempts to embed a semi-metal element oxide in quantumdots.

For example, the semi-metal element may include boron, silicon,germanium, arsenic, antimony, tellurium, fluorium, or a combinationthereof. For example, the semi-metal element may be silicon.

For example, the semi-metal element oxide may be silica.

When the oxides embedded in quantum dots are not semi-metal oxides butmetal oxides, compared with the semi-metal oxides, luminance of afinally-manufactured backlight unit is lower, thus it is aninsignificant effect of improving photo efficiency.

For example, the quantum dots may include Group 2-6 quantum dots such asCdSe, CdS, CdTe, ZnSe, ZnS, or ZnTe, Group 3-5 quantum dots such as InPor InAs, Group 4-6 quantum dots such as PbS, PbSe, PbTe, Group 4 quantumdots such as Ge or Si, Groups 1-3-6 quantum dots such asCu_(1-x)In_(x)S_(1-y)Se_(y) (0<x and y<1), or a combination thereof, butare not necessarily limited thereto.

For example, the quantum dot may have a core-shell structure, whereinthe core may be formed of Group 2-6 quantum dots, Group 3-5 quantumdots, Group 4-6 quantum dots, Group 4 quantum dots, a Group 1-3-6quantum dots, or a combination thereof, and the like, and the shell maybe a single shell, a double shell, or a triple shell.

Recently, since worldwide interest in the environment has been greatlyincreased, while regulations on toxic substances are being strengthened,environmentally-friendly cadmium-free quantum dots (InP/ZnS,InP/ZeSe/ZnS, and the like) may be used instead of quantum dots having acadmium-based core, and for example, when environmentally-friendlycadmium-free quantum dots have a core-shell structure, Groups 3 to 5quantum dots may be used as the core but are not necessarily limitedthereto.

For example, the quantum dots may have a perovskite crystal structure.

For example, the quantum dots may be a metal halide-based quantum dothaving a perovskite crystal structure. In this case, the quantum dotshaving the perovskite crystal structure may control the bandgap by themetal halide element. The bandgap energy of the quantum dots may beabout 1 eV to about 5 eV.

For example, the metal halide-based quantum dots having the perovskitecrystal structure may be represented by Chemical Formula 1, but are notnecessarily limited thereto.

ABX₃  [Chemical Formula 1]

In Chemical Formula 1,

A is an organic cation or an inorganic cation,

B is a metal cation, and

X is a halide anion.

For example, Chemical Formula 1 may be represented by CsPbX′₃, whereinX′ is Cl, Br, and/or I.

For example, the metal halide-based quantum dots having a perovskitecrystal structure may be green quantum dots having an average particlediameter of 1 nm to 8 nm or red quantum dots having an average particlediameter of 9 nm to 15 nm. In this case, the green quantum dots may berepresented by CsPbBr₃, and the red quantum dots may be represented byCsPb(BrI)₃.

For example, a size of the metal halide-based quantum dots having theperovskite crystal structure may be about 1 nm to about 900 nm. When themetal halide-based quantum dots having the perovskite crystal structurehave a size of greater than about 900 nm, there may be a fundamentalproblem that excitons may not reach light emission but may be separatedinto free charges and then disappear due to thermal ionization anddelocalization of charge carriers inside large nanocrystals.

For example, the quantum dots in which the semi-metal element oxide isembedded may be aerosolized. In other words, the quantum dots in whichthe semi-metal element oxide is embedded may be aerosolized and coatedon the light source configured to generate blue light. Herein, comparedwith when the quantum dots are coated without aerosolization, there maybe effects of shortening process time, reducing a thickness of a colorconversion layer, improving photo efficiency, and the like. In addition,when the quantum dots are aerosolized and coated on the blue OLEDsubstrate, the blue light leakage phenomenon may be completely blockedat a thickness of about 7 μm. Furthermore, when the quantum dots inwhich the semi-metal element oxide are embedded are aerosolized andcoated, the blue light leakage phenomenon may be completely blocked at athinner thickness, for example, at about 3 μm, and in addition, thephoto efficiency may be improved by about 40% or more, compared withwhen the semi-metal element oxide is coated without being embedded.

For example, the aerosolization may be carried out under vacuumconditions.

In an example embodiment, the quantum dots in which the semi-metalelement oxide are embedded may be prepared by mixing a precursormaterial of quantum dots and a semi-metal element oxide powder in asolvent, growing nanocrystals on the surface of the semi-metal elementoxide powder, and pulverizing them. In another example embodiment, thepre-synthesized quantum dots are mixed with the semi-metal element oxidepowder in the solvent, and the solvent is evaporated to adsorb or bondthe nanocrystals onto the surface of the semi-metal element oxide powderand pulverizing them.

Herein, the precursor material of the quantum dots or the semi-metalelement oxide powder mixed with the quantum dots may have a larger sizethan the quantum dots. For example, the semi-metal element oxide powdermay have a size of greater than or equal to about 300 nm and less thanor equal to about 2000 nm. On the other hand, when the quantum dots aremixed with the semi-metal element oxide powder, the quantum dots may bemixed in an amount of about 0.5 parts by weight to about 20 parts byweight based on about 100 parts by weight of the semi-metal elementoxide powder.

The process of coating by aerosolization of the quantum dots in whichthe semi-metal element oxide is embedded may be performed using anaerosol deposition apparatus.

As shown in FIG. 1 , an aerosol deposition device may include an aerosolchamber (not shown), a deposition vacuum chamber, a carrier gas supplymeans, a vacuum pump (not shown), and a nozzle. The aerosol chamber mayaccommodate the quantum dots and the semi-metal element oxide powder,and the light source configured to generate blue light, for example, theblue OLED substrate may be disposed in the deposit chamber. The carriergas supply means may supply carrier gas to the aerosol chamber, and thevacuum pump may make the deposition chamber in a vacuum state. Thenozzle may be disposed to be spaced apart from the substrate in thedeposition chamber and connected to the aerosol chamber through aconnection pipe. On the other hand, the aerosol chamber may be equippedwith a vibrator so that the nozzle may spray the composite powder in auniform aerosol form.

The aerosol deposition process makes the quantum dots and semi-metalelement oxide powder accommodated in the aerosol chamber, and when thecarrier gas is injected through the carrier gas supply means into theaerosol chamber, while the blue OLED substrate is disposed in thedeposition chamber, the quantum dots and the semi-metal element oxidepowders may be sprayed in an aerosol form through the nozzle onto theblue OLED substrate due to a pressure difference between the depositionchamber in a vacuum state and the aerosol chamber and thus form a thinfilm formed of the quantum dots in which the semi-metal element oxide isembedded on the blue OLED substrate.

In an embodiment, nitrogen (N₂) may be used as carrier gas of theaerosol deposition process.

Helium (He) is in general used as the carrier gas of the aerosoldeposition process. However, since helium has a small molecular weight,when helium gas is used as the carrier gas, the quantum dots and thesemi-metal element oxide powders collide with the substrate and otherpowders at a relatively high speed during the aerosol depositionprocess. In this way, when the quantum dots and the semi-metal elementoxide powders collide with the substrate or the other powders at arelatively high speed by the helium gas and thus receive high impactforces, the helium gas forms an electrically discharged plasma, and thisplasma may cause serious damage to the quantum dots and the semi-metalelement oxide powder, particularly, the quantum dots. In an actualaerosol deposition process, when the helium gas is used as the carriergas to spray the CsPbBr₃—SiO₂ composite powder onto a substrate, stronglight emission in local areas is observed, light emitted from a thinfilm formed through the aerosol deposition process has a blue-shiftedwavelength compared with light generated from the composite powderitself, resulting in lowering luminance intensity.

However, when nitrogen (N₂) is used as the carrier gas of the aerosoldeposition process as in the present invention, the nitrogen may notform the discharge plasma but solves the problems of damaging thequantum dots and the semi-metal element oxide powder, which aregenerated by using the helium gas as the carrier gas.

Since the aerosol deposition process is performed in the form ofhigh-speed jetting oxide powder particles with a size of about 1 μm,various factors such as types of carrier gas, particle shape, flow rateconditions of the carrier gas, nozzle design, and the like may causedeterioration, but since the quantum dots applied in one embodiment havea very small size (about 1 nm to about 15 nm), kinetic energy is nothigh enough to damage the quantum dots, thereby not causing thedegradation, but the high-speed jet method may be used to form a fairlydense film without pinholes, defects, and the like therein andcontribute to greatly reducing a thickness of the film.

On the other hand, an aerosol gas flow rate of the aerosolized quantumdots in which the semi-metal element oxide is embedded according to anexample embodiment of the present invention may be controlled to about0.1 L/min to about 10 L/min, for example, about 0.1 L/min to about 1.0L/min, for example, about 0.1 L/min to about 0.5 L/min, or for example,about 0.2 L/min to about 0.4 L/min. When the aerosol flow rate iscontrolled as above, an amount of impacts applied to the quantum dotsand the semi-metal element oxide powder may be sufficiently reduced, sothat the luminance intensity may not be lowered, and in addition,mechanical characteristics or optical properties of the thin film may benot deteriorated. In particular, when the aerosol gas flow rate iscontrolled as described above, luminescence characteristics amongoptical properties may be greatly improved. In addition, when the gasflow rate during the aerosolization is adjusted as described above, avery thin line width may be realized, so that a pattern process may beperformed without a mask.

The quantum dots in which the semi-metal element oxide is embedded mayhave a structure in which the quantum dots are uniformly dispersed in asemi-metal element oxide matrix, and may have a thickness of about 1 μmto about 50 μm.

For example, the light source configured to generate blue light may be ablue OLED, a blue LED, a blue EL device, and the like, but is notnecessarily limited thereto. For example, the light source configured togenerate blue light may be a direct light source unit including adiffusion plate and blue OLEDs disposed under the diffusion plate or anedge-type light source unit including a light guide plate and blue OLEDsdisposed on the side surface of the light guide plate.

The optical film is disposed on top of the light source configured togenerate blue light and may absorb a portion of the blue light, and thenconvert it into red light and green light.

For example, the optical film may include a first light conversion layerand a second light conversion layer.

The first light conversion layer may absorb the blue light from thelight source and then convert it into the red light. In an embodiment,the first light conversion layer may have a structure in which redquantum dots are dispersed in a first semi-metal element oxide matrix.The first semi-metal element oxide matrix may be formed of silica. Thered quantum dots may be metal halide-based quantum dots having theperovskite crystal structure.

The second light conversion layer is formed on the first lightconversion layer and may absorb blue light from the light source andthen convert it into green light. In an embodiment, the second lightconversion layer may have a structure that green quantum dots aredispersed in a second semi-metal element oxide matrix. The secondsemi-metal element oxide matrix may also be formed of silica. The greenquantum dots may be metal halide-based quantum dots having theperovskite crystal structure.

In an embodiment, the optical film 120 may be formed by sequentiallyforming the first light conversion layer 122 and the second lightconversion layer 123 on the substrate 121 through the aerosol depositionmethod.

The first light conversion layer may be formed on the light source bypreparing first composite powder of the red quantum dots and the firstsemi-metal element oxide, and then controlling the aerosol gas flow ratethereof in the aerosol deposit method using nitrogen as the carrier gas.

The second light conversion layer may be formed on the light source bypreparing the second composite powder of the green quantum dots and thesecond semi-metal element oxide and then controlling the aerosol gasflow rate thereof in the aerosol deposit method using nitrogen as thecarrier gas.

Since an optical film applied to a backlight unit according to thepresent invention has a structure of including quantum dots dispersed ina semi-metal element oxide matrix, particularly, metal halide-basedquantum dots having a perovskite crystal structure, excellent long-termstability against external heat, moisture, and stress may be obtained,and since being formed by controlling an aerosol gas flow rate, a finepattern process may not only be performed without a mask, but excellentmechanical and optical properties may also be obtained.

Another embodiment provides a down-conversion medium including thebacklight unit.

The down-conversion medium may be a color filter-free down-conversionmedium, that is, a down-conversion medium that does not include a colorfilter.

Another embodiment provides a display device including thedown-conversion medium.

Hereinafter, the present disclosure is illustrated in more detail withreference to examples, but these examples are not in any sense to beinterpreted as limiting the scope of the disclosure.

<Manufacture of Backlight Unit>

Example 1

A mechanical rotary pump was used to create an almost complete vacuum ina chamber, and cadmium-free perovskite quantum dots (PeQD) film weredeposited by using a UAD at room temperature (25° C.) under a pressureof 10⁻¹ torr. After mixing TOPO-Zn CsPbBr₃ (green) and TOPO-ZnCsPb(BrI)₃ (red) quantum dots as light conversion layer materials inn-hexane respectively at a concentration of 64 mg per 100 ml, silicapowder was infiltrated through a fine sieve (ASTM mesh No. 170). Theprepared green and red materials were respectively disposed in differentaerosol chambers. An ultrasonic nebulizer (1.8 MHz) and a N₂ carrier gasinjected at a rate of 1 L/min were used to generate aerosolized dropletsof the PeQD solution, starting to deposit clean PeQD (green or red). Asfor a system containing a mixture of PeQD and semi-metal element oxideof silica, two constituent elements were allowed to converge into anozzle from each aerosol chamber for the subsequent codeposition. Inorder to control a feed rate of PeQD and the silica, a mass flow ratecontroller was adjusted to control a flow rate of aerosol gas to 0.3L/min by using the N₂ carrier gas, and the ultrasonically-generated PeQDaerosol was made to quickly pass through an orifice nozzle (with adiameter of 1 mm) due to a pressure difference between the aerosol andthe deposition chamber under the carrier gas flow. This aerosol wasrapidly sprayed onto a BOLED substrate 5 mm away from the nozzle.Subsequently, a substrate holder attached to the BOLED substrate wasautomatically moved along an XY plane at a scan speed of 5 mm/s. As aresult, a PeQD layer or a PeQD-silica composite layer was denselydeposited on the BOLED substrate. A film thickness of the layer waschanged by adjusting a concentration of PeQD and the number of scans. Inorder to block blue light, a light conversion layer was deposited at thePeQD (green and red) concentration of 64 mg/100 ml and 3 to 4 scans.

Example 2

A cadmium-free perovskite quantum dot (PeQD) film was deposited in thesame manner as in Example 1, except that the flow rate of aerosol gaswas changed to 0.1 L/min instead of 0.3 L/min.

Example 3

A cadmium-free perovskite quantum dot (PeQD) film was deposited in thesame manner as in Example 1, except that the flow rate of aerosol gaswas changed to 0.5 L/min instead of 0.3 L/min.

Comparative Example 1

A cadmium-free perovskite quantum dot (PeQD) film was deposited in thesame manner as in Example 1, except that the silica powder was not used.

Comparative Example 2

A cadmium-free perovskite quantum dot (PeQD) film was deposited in thesame manner as in Example 1, except that alumina (α-Al₂O₃) was usedinstead of the silica powder.

<Evaluation>

Referring to FIGS. 2 and 3 , green quantum dots and red quantum dotswere all deposited on a BOLED substrate.

Referring to FIGS. 4 to 6 , green quantum dots, alumina-embedded greenquantum dots, and silica-embedded green quantum dots were well depositedon a BOLED substrate (glass). FIG. 4 shows a photograph of ComparativeExample 1, FIG. 5 shows a photograph of Comparative Example 2, and FIG.6 shows a photograph of Example 1.

Referring to FIGS. 7 to 9 , red quantum dots, alumina-embedded redquantum dots, and silica-embedded red quantum dots were well depositedon a BOLED substrate (glass). FIG. 4 shows a photograph of ComparativeExample 1, FIG. 5 shows a photograph of Comparative Example 2, and FIG.6 shows a photograph of Example 1.

FIG. 10 is a graph showing green photo efficiency of backlight unitsaccording to Example 1 and Comparative Examples 1 and 2, and FIG. 11 isa graph showing red photo efficiency of the backlight units according toExample 1 and Comparative Examples 1 and 2. Accordingly, the backlightunits according to Example 1 and Comparative Examples 1 and 2 exhibitedequivalent photo efficiency, but the backlight unit of Example 1exhibited excellent wavelength compatibility, compared with thebacklight units according to Comparative Examples 1 and 2.

FIG. 12 is a graph showing green luminance of the backlight unitsaccording to Example 1 and Comparative Examples 1 and 2, and FIG. 13 isa graph showing red luminance of the backlight units according toExample 1 and Comparative Examples 1 and 2. Accordingly, the backlightunit according to Example 1 had excellent luminance compared with thebacklight units according to Comparative Examples 1 and 2.

FIG. 14 is a graph showing luminance (green) of the backlight unitaccording to Example 2, FIG. 15 is a graph showing luminance (green) ofthe backlight unit according to Example 1, and FIG. 16 is a graphshowing luminance (green) of the backlight unit according to Example 3,which shows that the closer an aerosol gas flow rate was to 0.3 L/min,the better luminescence characteristics were and that the aerosol gasflow rate could be controlled to improve luminance of a backlight unit.

While this invention has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. Therefore, the aforementioned embodimentsshould be understood to be exemplary but not limiting the presentinvention in any way.

What is claimed is:
 1. A backlight unit, comprising a light sourceconfigured to generate blue light; and an optical film configured toabsorb a portion of the blue light generated from the light source togenerate red light and green light, wherein the optical film includes aquantum dot matrix in which a semi-metal element oxide is embedded. 2.The backlight unit of claim 1, wherein the semi-metal element comprisesboron, silicon, germanium, arsenic, antimony, tellurium, fluorium, or acombination thereof.
 3. The backlight unit of claim 2, wherein thesemi-metal element oxide is silica.
 4. The backlight unit of claim 1,wherein the quantum dot comprises Group 2-6 quantum dots, Group 3-5quantum dots, Group 4-6 quantum dots, a Group 4 quantum dot, Group 1-3-6quantum dots, or a combination thereof.
 5. The backlight unit of claim1, wherein the quantum dots have a perovskite crystal structure.
 6. Thebacklight unit of claim 5, wherein the quantum dots have a perovskitecrystal structure.
 7. The backlight unit of claim 6, wherein the metalhalide-based quantum dots having the perovskite crystal structure isrepresented by Chemical Formula 1:ABX₃  [Chemical Formula 1] wherein, in Chemical Formula 1, A is anorganic cation or inorganic cation, B is a metal cation, and X is ahalide anion.
 8. The backlight unit of claim 7, wherein Chemical Formula1 is represented by CsPbX′₃, wherein X′ is Cl, Br, and/or I.
 9. Thebacklight unit of claim 7, wherein the metal halide-based quantum dotshaving the perovskite crystal structure is green quantum dots or redquantum dots.
 10. The backlight unit of claim 9, wherein the greenquantum dots are CsPbBr₃ and the red quantum dot are CsPb(BrI)₃.
 11. Thebacklight unit of claim 1, wherein the quantum dot matrix in which thesemi-metal element oxide is embedded is aerosolized.
 12. The backlightunit of claim 11, wherein the aerosolization is carried out under vacuumconditions.
 13. The backlight unit of claim 11, wherein an aerosol flowrate during the aerosolization is about 0.1 L/min to about 10 L/min. 14.The backlight unit of claim 1, wherein the light source configured togenerate blue light is a blue OLED, a blue LED, or a blue EL device. 15.A down-conversion medium comprising the backlight unit of claim
 1. 16.The down-conversion medium of claim 15, wherein the down-conversionmedium is a color filter-free down-conversion medium.
 17. A displaydevice comprising the down-conversion medium of claim 15.